In general, as a method for forming a hollow in a synthetic resin molded body, a blow molding method is most well known and widely used in production of bottles, containers, pipes, and the like. However, there are many design restrictions in the blow molding method, the selection of adaptable materials is limited, and further there is such a problem that the dimensional accuracy is not very good.
Thus, in recent years, various hollow molding methods using injection molding are proposed and include a lost core method, a two-shell molding/welding method, and a die slide injection molding method (see, Patent Literature 1). However, it is difficult to produce a long three-dimensionally bent pipe having a bent portion, using those molding methods.
As a molding method for solving the above problems, a method using a floating core is known (Patent Literatures 1 to 3).